Chem 181: Experiment 4
Physical and Chemical Properties and
Changes
Chemistry is the study of matter. It is very common for a chemist to need to describe a
bit of matter as thoroughly as possible. In doing so, the chemist would certainly list physical
properties. Many physical properties can be observed using our senses: color, crystal shape, and
phase at room temperature are some examples. Other physical properties involve quantitative
observations and so must be measured; density, specific heat capacity, and boiling point are three
examples. A physical change is any change in a substance that does not involve a change in its
chemical composition. During a physical change, no new chemical bonds are formed, and so the
chemical composition remains the same. Examples of physical change are boiling, freezing,
expanding, and dissolving.
Matter can also be characterized by its chemical properties. The chemical properties of a
substance include all the chemical changes possible for that substance. A chemical change is
one in which the substance is transformed to a new substance. That is, there is a change in the
chemical composition of the substance. During a chemical change, the atoms are pulled apart
from one another, rearranged, and put back in a new arrangement. Examples of chemical change
are burning, rusting, fermenting, and decomposing.
In this experiment, you will observe chemical reactions that are characteristic of various
compounds under controlled conditions. After collecting and organizing your data, you will then
perform the same tests on four unknown compounds to identify them.
What observations will you be looking for? Chemical changes are generally accompanied
by one or more of the following:
• A gas is evolved. This evolution may be quite rapid, or it may be a “fizzing” sound.
• A precipitate appears (or disappears). The nature of the precipitate is important. It may be
crystalline, it may have color or it may merely cloud the solution.
• Heat may be evolved or absorbed. The reaction vessel becomes warm if the reaction is
exothermic or cools if the reaction is endothermic.
• A color change occurs. A substance added to the system may cause a color change.
• A change in odor is detected. The odor of a substance may appear, disappear, or become more
intense during the course of a chemical reaction.
The chemical properties of the following compounds, dissolved in water, are investigated in this
experiment:
Sodium chloride
Sodium carbonate
Magnesium sulfate
Barium chloride
Water
NaCl(aq)
Na2CO3(aq)
MgSO4(aq)
BaCl2(aq)
H2O(l)
The following test reagents are used to identify and characterize these compounds:
Silver nitrate
Sodium hydroxide
Sulfuric acid
AgNO3(aq)
NaOH(aq)
H2SO4(aq)
OBJECTIVE
•
To identify a compound on the basis of its chemical properties.
MATERIALS
Disposable pipettes
Small test tubes
Test tube rack
0.2 M Sulfuric Acid
0.2 M Sodium Hydroxide
0.2 M Sodium Carbonate
0.2 M Magnesium Sulfate
0.1 M Barium Chloride
0.2 M Sodium Chloride
0.2 M Silver Nitrate
PROCEDURE
1. Obtain and wear goggles.
2. Label five small clean test tubes (figure 1).
Place approximately 20 drops of each of the five
known solutions into the labeled test tube.
Figure 1. Label each test tube with the
reagent being tested and add silver
nitrate to each.
3. Use the dropper to deliver several drops of the
silver nitrate solution to each of the known
solutions. (Caution: AgNO3 forms black stains
on the skin. The stain, caused by silver metal,
causes no harm.)Record your observations on the report sheet. Your list of choices for the
report sheet are:
a. Write “Precip” if a precipitate forms
b. Write “Color” if you see a color change without any precipitate formation.
c. Write “Gas” if there are bubbles/gas formation.
d. Write “Odor” if there is a gas with an odor.
e. Write “NR” if there is no reaction.
4. Dispose of the solutions in the test tubes. Place the solutions in the waste beaker in the
hood. Clean the test tubes to use them for the next part of the experiment.
5. Repeat steps 2-5 except use the dropper bottle of NaOH instead of AgNO3.
6. Repeat steps 2-5 except use the dropper bottle of H2SO4 instead of AgNO3.
7. Repeat steps 2-7 except using the four unknown solutions instead of the five known
solutions
Report Sheet Exp.4 Physical and Chemical Properties
Name:
Date:
Lab Section:
Partner’s Name:
Compound
AgNO3
NaOH
H2SO4
NaCl
Na2CO3
MgSO4
BaCl2
H2O
Unknown #1
Unknown #2
Unknown #3
Unknown #4
Identity of Unknowns
Unknown #1
Unknown #2
Unknown #3
Unknown #4
Write a balanced chemical equation for each reaction where a determination of a reaction occurs.